Back in the 1980s, I had a video about research into dolphin communication put together by Jacques Cousteau. In it, there was a section on Silbo, a whistling language used in the Canary Islands off Spain to communicate long distance (it was meant to show that you could communicate effectively through whistling. Well, bless the Canary Islands, because they’re making sure that Silbo sticks around. Nice article, and it has an audio file of an interaction in Silbo, plus its translation.